1. Field of the Invention
The invention relates to a method for manufacturing a composite strip, coated with a tin-silver alloy, for producing electrical contact components.
2. Description of Related Art
Tin-silver is a very good contact material. It is characterized principally by its low electrical resistance, its hardness, and its abrasion resistance.
The possibilities for coating an electrically conductive base material with a tin-silver alloy by electroplating are, however, limited. U.S. Pat. No. 5,514,261 discloses in this connection a way to deposit a silver-tin alloy by electroplating from a cyanide-free bath. The bath is prepared using silver as the nitrate or diamine complex, tin as a soluble tin(II) or tin(IV) compound, and mercaptoalkane carboxylic acids and sulfonic acids. Films of silver-tin alloys with a silver content of approximately 20 wt % to 99 wt % can be deposited from this bath.
The silver concentration of a coating manufactured in this manner is relatively high; films with lower silver concentrations cannot be attained. In addition, the film generated by electroplating is finely banded, with a slight micro-roughness. The film is brittle, and will tolerate only small bending stresses.